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#V2X#C-V2X#DSRC#자율주행#C-ITS
Last updated · 2026-10-23

V2X (Vehicle-to-Everything)

1. Overview

Definition: V2X (Vehicle-to-Everything) refers to vehicular communication technology in which a vehicle wirelessly exchanges driving-situation information with every surrounding entity — other vehicles, road infrastructure, pedestrians, and the network — thereby extending the driver's field of perception beyond the line of sight (visual and sensor range).

As autonomous driving and Intelligent Transport Systems (ITS) have advanced, the limits of relying on a vehicle's own sensors alone (camera, LiDAR, radar) have become clear. Sensors are fundamentally Line-of-Sight based, so they cannot detect Non-Line-of-Sight hazards such as a pedestrian stepping out from behind a building corner, a hard-braking vehicle hidden by the car ahead, or a work zone beyond a curve. V2X complements this limitation through communication. When surrounding vehicles and infrastructure periodically broadcast their position, speed, heading, and braking state, a receiving vehicle can recognize hazards in areas its sensors cannot reach through cooperative awareness and prevent collisions in advance.

A major driver behind its emergence was the social demand to reduce traffic accidents. The U.S. National Highway Traffic Safety Administration (NHTSA) has estimated that V2V communication alone could prevent a substantial share of crashes such as intersection collisions and rear-end accidents, which became the key rationale for countries to allocate the 5.9 GHz band exclusively for transport safety. In addition, as autonomous driving rises to Level 3 and beyond, intention sharing and cooperative driving among vehicles become essential, so V2X has established itself as the "invisible sensor" of autonomous driving and as essential infrastructure. Its characteristics can be summarized as follows: (1) low latency (safety messages within tens of ms) and high reliability, (2) support for direct device-to-device communication without a cellular base station, and (3) a premise of a public-key-infrastructure (PKI) security scheme that protects privacy.

2. V2X Communication Types and Overall Structure

V2X is classified into four types by communication counterpart, and these combine to form a single cooperative transport ecosystem. The overall structure is as follows.

graph TB
    subgraph Road["Roadside field"]
        V1["Vehicle A (OBU)"]
        V2["Vehicle B (OBU)"]
        P["Pedestrian (smartphone)"]
        RSU["Road Side Unit (RSU)"]
        SIG["Traffic signal/sign"]
    end
    subgraph Net["Network/cloud"]
        BS["Base station (gNB/eNB)"]
        TMC["Traffic Management Center (TMC)"]
        SCMS["Security system (SCMS/PKI)"]
    end
    V1 ---|"V2V (direct)"| V2
    V1 ---|"V2P"| P
    V1 ---|"V2I"| RSU
    RSU --- SIG
    V1 ---|"V2N"| BS
    BS --- TMC
    RSU --- TMC
    SCMS -.->|"issues certificates"| V1
    SCMS -.->|"issues certificates"| RSU

A. V2V (Vehicle-to-Vehicle) is the type where vehicles communicate directly with one another. Each vehicle broadcasts a BSM (Basic Safety Message, U.S.) or CAM (Cooperative Awareness Message, Europe) about 10 times per second (10 Hz) to share position, speed, acceleration, steering angle, and so on. This enables safety services such as Forward Collision Warning (FCW), Blind Spot Warning (BSW), and Intersection Movement Assist (IMA). For example, when the car ahead brakes hard, that state is propagated immediately, so a following vehicle can receive a warning before the driver even sees the brake lights.

The value of V2V lies in the "proactive sharing of intention" that sensors cannot achieve. A camera or radar can only measure the car ahead after it actually decelerates, whereas V2V broadcasts the event itself the moment the brake pedal is pressed, so the warning propagates before the physical motion appears. In a multi-vehicle (chain) collision, those few hundred milliseconds of lead time shorten braking distance and greatly reduce the scale of the accident. Moreover, on curves and at intersections where the sensor line of sight is blocked, V2V becomes effectively the only means of advance recognition, so it is regarded as a core axis for securing the safety margin of autonomous driving.

B. V2I (Vehicle-to-Infrastructure) is communication between a vehicle and road infrastructure such as a Road Side Unit (RSU) or traffic signal. Representative services include red-light violation warning, provision of signal remaining time (SPaT, Signal Phase and Timing), and work-zone/debris warning. When an RSU at an intersection broadcasts signal-phase information, the vehicle adjusts its speed to the green signal through GLOSA (Green Light Optimal Speed Advisory), reducing hard acceleration/braking to improve fuel economy and emissions.

C. V2P (Vehicle-to-Pedestrian) is communication between a vehicle and smartphones/wearables carried by vulnerable road users such as pedestrians and cyclists. In school zones or back streets, it alerts the vehicle to the pedestrian's position to prevent collisions with pedestrians in Non-Line-of-Sight areas. V2P faces challenges in device battery drain and GNSS positioning error (several to tens of meters in urban canyons), but it carries great social value for protecting vulnerable road users and is expanding in combination with smart-crosswalk and school-zone pilot projects.

D. V2N (Vehicle-to-Network) is the type where a vehicle communicates with a traffic management center/cloud via a cellular base station. It handles wide-area, high-volume services such as wide-area traffic information, Over-The-Air (OTA) software updates, and HD Map reception. If V2V/V2I are responsible for the safety of "here and now," V2N handles the efficiency of "wide areas and future road segments," complementing one another.

Type Counterpart Representative service Latency requirement Communication nature
V2V Vehicle↔Vehicle FCW·BSW·IMA ~20 ms, very low Direct (broadcast)
V2I Vehicle↔RSU/signal SPaT·GLOSA·work-zone warning Low Direct
V2P Vehicle↔pedestrian device Pedestrian collision warning Low Direct
V2N Vehicle↔base station/cloud Traffic info·OTA·HD Map Relatively relaxed Via network

3. Communication Technology: DSRC (WAVE) vs C-V2X

The underlying radio technologies that implement V2X have evolved along two broad families, and the two differ fundamentally in physical-layer design philosophy. Below is the detailed structure from a protocol/interface perspective.

graph LR
    subgraph DSRC["DSRC / WAVE family"]
        D1["App: SAE J2735 (BSM)"]
        D2["Security: IEEE 1609.2"]
        D3["Network: IEEE 1609.3 (WSMP)"]
        D4["PHY/MAC: IEEE 802.11p"]
        D1 --> D2 --> D3 --> D4
    end
    subgraph CV2X["C-V2X family"]
        C1["App: SAE J2735 (BSM)"]
        C2["Security: IEEE 1609.2"]
        C3a["PC5 interface (direct device/sidelink)"]
        C3b["Uu interface (via base station)"]
        C4["PHY: LTE-V2X(R14) -> 5G NR-V2X(R16)"]
        C1 --> C2 --> C3a --> C4
        C2 --> C3b --> C4
    end

A. DSRC (Dedicated Short-Range Communications) is based on the Wi-Fi-family IEEE 802.11p, and in the U.S. it is standardized — bundling the upper layers — as the WAVE (Wireless Access in Vehicular Environments) standards family (IEEE 1609.x + SAE J2735). Because vehicles can communicate instantly without a base station, field validation was commercialized earliest in the early 2010s. However, it was criticized for the Wi-Fi-based media access being vulnerable to collisions/congestion under high-density traffic, and for relatively limited range and mobility.

B. C-V2X (Cellular V2X) is the cellular-based scheme standardized by 3GPP. Its core is two interfaces. PC5 (sidelink) handles direct device-to-device communication without a base station, replacing DSRC's V2V/V2I role, while Uu handles V2N over the existing cellular network. It began with LTE-V2X in Release 14 in 2017, and evolved in 5G NR-V2X in Release 16 in 2020 to support ultra-low latency and high reliability (URLLC), platooning, and advanced cooperative driving. In particular, NR-V2X supports unicast and groupcast and introduces HARQ retransmission on the sidelink to raise reliability.

The key difference between the two schemes lies in media access and evolution path. DSRC uses unlicensed contention-based access, so performance degrades sharply under congestion, whereas C-V2X's PC5 reserves resources via Semi-Persistent Scheduling (SPS), remaining stable even at high density. The more important practical implication is continuity of generational evolution. C-V2X naturally upgrades LTE→5G and can directly leverage the mobile-communication ecosystem, chipsets, and investment, so regulators are increasingly converging on C-V2X.

Category DSRC (WAVE) C-V2X
Base technology IEEE 802.11p (Wi-Fi family) 3GPP LTE/5G
Direct communication Single (contention-based) PC5 sidelink (SPS reservation)
Network communication Separate (cellular alongside) Uu (same ecosystem)
Evolvability Limited LTE-V2X→5G NR-V2X continuous
High-density performance Vulnerable Relatively superior
Commercialization timing Early mover Later but spreading fast

4. V2X Security Scheme (SCMS / C-ITS PKI)

Because V2X handles safety messages directly tied to human life, it must simultaneously achieve protection against message forgery/tampering and protection of sender privacy. To this end, messages are protected by digital signatures in the IEEE 1609.2 format, and the system that issues and manages the certificates for trusting these signatures is the U.S. SCMS (Security Credential Management System) and the European C-ITS PKI.

The core design principles are the pseudonym certificate and separation of duties. Instead of a long-term fixed ID, a vehicle is issued many short-lived pseudonym certificates and uses them in rotation. This makes it difficult for an external attacker to collect messages and track a specific vehicle's travel route. At the same time, SCMS separates functions and operating entities into a Registration Authority (RA), Pseudonym Certificate Authority (PCA), Linkage Authority (LA), and so on, so that no single entity alone can know "which pseudonym belongs to which vehicle." Identifying and revoking a specific vehicle is possible only when multiple entities collude, making it strong even against insider threats. In the actual U.S. scheme, a vehicle is preloaded with three years' worth of certificates and rotates numerous pseudonym certificates on a weekly basis.

Component Role
RA (Registration Authority) Device registration and certificate-request relay; requester anonymization
PCA (Pseudonym Certificate Authority) Issuance of short-lived pseudonym certificates
LA (Linkage Authority) Distributed storage of certificate-device linkage values (recovery upon revocation)
MA/CRL Detection of misbehaving devices and distribution of the certificate revocation list

The U.S. SCMS and Europe's C-ITS PKI share the goal of "pseudonym-based privacy protection" but differ in issuance structure. SCMS maximizes separation of duties so that re-identification is impossible without collusion of multiple entities, whereas the ETSI-based European scheme adopts a relatively simple two-stage structure of Enrollment Authority (EA) and Authorization Authority (AA). Such design differences stem from differences in operational complexity, regulatory environment, and operator structure, and lead to a practical implication of making cross-certification (mutual trust) difficult when vehicles move across multiple countries (roaming). Even if the IEEE 1609.2 certificate format is shared, if the root of trust and policy differ, cross-border message verification does not hold.

However, if the pseudonym rotation period is too long it is vulnerable to tracking, and if too short it increases certificate issuance/verification load and storage capacity — a privacy-performance trade-off. In addition, the scalability of verifying/revoking the certificates of tens of millions of vehicles in real time, and how quickly misbehaving/malicious vehicles can be excluded via the CRL, remain core design challenges. Since signature-verification computation must be performed for every message from numerous vehicles flooding in at 10 Hz, the HSM (hardware security module)/accelerator performance of the device and strategies for verification omission/prioritization must also be considered.

5. Comparison and Cases: Technology Convergence and Domestic/International Trends

The conclusion of the technology competition is revealed in each country's spectrum policy. The U.S. FCC decided in 2020 to reorganize the 5.9 GHz band (5.850–5.925 GHz), opening the lower 45 MHz for unlicensed (Wi-Fi) use and reducing the ITS portion to the upper 30 MHz, and effectively adopted C-V2X rather than DSRC as the technology for the ITS band. Subsequently, in November 2024, the FCC adopted final C-V2X rules, setting operational details (e.g., using three 10 MHz channels separately or combined into 20 MHz or 30 MHz) and providing for a sunset of existing DSRC over roughly a two-year grace period. The final rule's effective date was announced as early 2025. This symbolizes an international turning point in which DSRC — which had led for over a decade — converges onto C-V2X.

Domestically, C-ITS (Cooperative Intelligent Transport System) demonstration projects have proceeded, centered on the Ministry of Land, Infrastructure and Transport and ITS-related organizations. Initially, RSUs were deployed on highways and in demonstration cities centered on WAVE (DSRC), but considering the global C-V2X convergence trend and the strength of 5G infrastructure, debate over the communication method continued. IEEE 1609.2-based certificates have been commonly adopted in the U.S., Europe (ETSI profile), China (CCSA), Korea, and elsewhere, so the security layer is in a relatively internationally converged state.

To give a concrete sense of numbers, safety messages (BSM/CAM) are transmitted at a 10 Hz cycle, and services such as intersection collision warning require delivery and response within tens of ms. In platooning, narrowing the inter-vehicle gap reduces air resistance and can improve the fuel economy of heavy trucks by a few percent; safely maintaining that short gap presupposes the low-latency, high-reliability direct communication of C-V2X.

6. Deep Dive: Cooperative Automated Driving and 5G NR-V2X Evolution

The core of the latest trend is V2X evolving beyond simple "warning alerts" into the foundation of Cooperative Automated Driving. 5G NR-V2X (3GPP Release 16 and beyond) is designed to target advanced services such as Maneuver Sharing/Coordination (intention/trajectory sharing), platooning, and sensor-data sharing (Collective Perception). For example, if vehicles at an intersection exchange their planned driving trajectories in advance and negotiate the order of passage, a futuristic intersection control becomes possible in which the intersection is cleared without collisions even without traffic signals.

Another axis is the extension of sensor fusion. If objects recognized by an individual vehicle's LiDAR/camera are shared via V2X, then even in environments where sensors are weak (fog, nighttime), Collective Perception (Collective Perception Message, CPM) becomes possible, borrowing the "eyes" of surrounding vehicles and infrastructure to widen the perception range. This is the core mechanism by which an autonomous vehicle complements the limits of its own sensors through communication. Furthermore, combining with MEC (Mobile Edge Computing) to process road video/sensor data at the edge can greatly reduce the latency of V2N-based services to support real-time cooperative driving. Likely exam directions include: (1) the comparison of DSRC vs C-V2X and the rationale for convergence, (2) the privacy-protection principles of SCMS (pseudonym certificates, separation of duties), and (3) the changing role of V2X as the autonomous-driving level rises.

7. Considerations and Implications

From a professional engineer's perspective, the following must be considered comprehensively when adopting and deploying V2X.

A. Communication-method selection strategy (interoperability): New infrastructure investment should reflect the international convergence trend (C-V2X) and the evolvability of 5G, while also designing a transition roadmap and grace period alongside already-deployed DSRC assets. As in the U.S. FCC's two-year sunset case, without backward compatibility and a phased transition plan, existing investment becomes stranded.

B. Security-privacy trade-off: The pseudonym rotation period, certificate preload volume, and CRL distribution cycle are balancing points between tracking resistance and verification load/storage capacity. One must have a scalable PKI capable of operating the certificate lifecycle at the scale of tens of millions of vehicles, together with a system for the rapid revocation of misbehaving vehicles.

C. Safety and reliability assurance: Because safety messages' latency of tens of ms and high reliability are directly tied to life, congestion control under high-density traffic (DCC, Decentralized Congestion Control) and resource management that guarantees low latency are essential. A fail-safe design that operates safely with the vehicle's own sensors even during communication loss/errors must be a prerequisite.

D. Ecosystem and legal/institutional linkage: V2X is a multi-party ecosystem entangling vehicle manufacturers, carriers, road authorities, and security agencies, so institutional arrangements such as spectrum allocation, personal-data protection, and liability for accidents determine the speed of technology diffusion. A standards/governance strategy aligned with the autonomous-driving advancement roadmap is as important as the technology itself.

E. Use of related technologies: Integrated design with adjacent technologies — 5G URLLC/network slicing, MEC, HD Map/precise positioning (GNSS correction), Collective Perception (CPM) — determines the effectiveness of V2X.

F. Phased diffusion and the penetration-rate challenge: The safety effect of V2V has a network effect that grows in proportion to the share of communication-equipped vehicles. Early on, the equipment rate is low so the perceived effect is small, so a transition strategy is needed to pass critical mass through mandatory installation on new vehicles, up-front investment in infrastructure (RSUs), and distribution of V2P devices. In this process, a phased deployment that first provides utility through V2N/cloud-based services while waiting for the direct-communication ecosystem to mature becomes a realistic alternative.

References

In one line: V2X is a technology by which a vehicle exchanges information at low latency and high reliability with surrounding vehicles (V2V), infrastructure (V2I), pedestrians (V2P), and the network (V2N) to perceive even Non-Line-of-Sight hazards; it is converging from DSRC to C-V2X (5G NR-V2X) and protects privacy with SCMS-based pseudonym certificates, serving as core infrastructure for autonomous driving.